A casket bearing the body of Sarai Sierra is carried to an ambulance in Istanbul Feb. 6. The man at left is holding a photo of the slain 33-year-old New York woman. / AP

by Yasemin Ergin and Victor Kotsev, Special for USA TODAY

by Yasemin Ergin and Victor Kotsev, Special for USA TODAY

ISTANBUL - Turkish police told USA TODAY they are searching for a man they believe was involved in the killing of a New York mother of two who was found dead nearly two weeks after being reported missing in January.

The man - identified only as Ziya T. and described as homeless, "unstable" and selling trash for a living - was spotted on video selling Sarai Sierra's blood-stained leather jacket at a flea market in Istanbul shortly after her body was found, police said.

"There is incriminatory evidence linked to this man, and our police department is doing everything in their power to find him so we can obtain DNA samples from him and have clarity," Istanbul prosecutor Huseyin Kaplan said.

"I am not supposed to give away details about an ongoing investigation," Kaplan said, "but there is a lot of wrong information floating around, so I want to straighten out what we have."

Ziya T.'s brother, whose identity was confirmed by police as Hamdi T., 50, told police he had received a phone call from his brother on Feb. 9. Hamdi told police that Ziya said he was leaving Istanbul to go to Hatay province in southeastern Turkey and maybe even crossing the border to Syria.

To help investigators, Hamdi submitted a DNA sample, which showed similarities to the DNA found on Sierra's body, making the case against his brother even stronger, police officials confirmed.

In an interview with the Turkish daily Hurriyet, Hamdi said he had called on his brother to surrender, adding that "I gave every kind of assistance to the police for them to find my brother."

Turkish police have posted his photograph at border crossings in the southeastern part of the country and are conducting an extensive manhunt in Hatay province.

Sierra, 33, a budding photographer, flew to Turkey Jan. 7 to spend a few weeks capturing images of the bridges and monuments of Istanbul and other European cities. She disappeared on Jan. 21, the day before she was due to fly home to New York. It was her first trip outside the United States, one she described as her "dream" trip.

Her husband, Steven Diaz Sierra, and her brother, David Jimenez, flew to Turkey to assist with the search. Her body was found Feb. 2 near a deserted part of the ancient city walls in the center of Istanbul - an area frequented by the homeless. The medical examiner ruled she had died from a blow to the head.

She was found wearing only underwear and a shirt, but initial autopsy reports showed no evidence of sexual assault. Investigators believe that she tried to defend herself because they found skin particles under her fingernails.

Police found a bloody brick near the city walls, and the blood on it matched Sierra's. Police officials also said Ziya T. was not among the individuals from whom they obtained DNA samples. They did take a sample from a man - identified only as "Taylan" - with whom she had been corresponding for four months via social networks. Sierra was supposed to meet him on Galata Bridge the day she disappeared.

The investigation surrounding Sierra's death quickly became one of Istanbul's most high-profile murder cases. Police assigned 230 investigators to it, first in a massive missing-person search, then in a large-scale hunt for her killer. Close to 30 people were questioned in the course of the investigation, and DNA samples were obtained from all of them.

Before word of the current suspect emerged, published reports about Sierra involving relationships with men and extravagant expenses - as well a trip to Amsterdam during her vacation - raised questions about the circumstances of her disappearance and death.

Ertan Ercikti, an Istanbul police chief overseeing the homicide department, complained in an interview that the intense media attention on the woman's disappearance and the rumors surrounding her death added to the difficulties of the investigators.

"I would rather focus on facts and on the evidence we have at hand, instead of responding to all this speculation," Ercikti said a few days after Sierra's body was found, referring to unconfirmed newspaper reports stating that FBI agents believed that Sierra had spent time with "criminal elements" in Istanbul.

He added that "it is very unlikely that she was killed someplace else and then carried to the scene (where they found her)," which is why police almost completely focused on those known to hang around in the area.